Method of molding silica



y o L. B. MILLER METHOD 0F MOLDING SILICA Filed Nov. 24, 1925' PatentedMay 10, 1927.

UMTED'sTATEsv -Pari-:lar OFFICE.

LEVI 13. MILLEa-OELYN'N, MASSACHUSETTS, ASSIGNOE To GENERAL ELECTRICCOMPANY, A CORPORATION or N-Ew YORK.

METHOD F HOLDING SILICA..

i Application led November 2e, 1925. Serial No. 71,245.

The present invention relates to the moldlng or shaping of vitreousslllca and its object is to produce articles of regular formv such, forexample, as cylindrical bodies of silica having av smooth surface and inparticular to 'reduce thick -walled tubular blanks of si ica, which areadapted to be drawn out into long, thin walled tubing.

Although it is practicable to carry out the fusion of silica in agraphite container without undulyV contaminating the silica by theformation of carbon compounds, Some difficulty is experienced 'due tothe sticking of carbon to the surface of the solidified l5 mass, as itsremoval leaves irregularities in the surface of the product. When thefused silica is to be employed for the subsequent -fabricationofarticles, 'for example by cutting lup the solidified' mass of silicainto plates or by extruding it when plastic througha die, then nodiiiicultyis experienced with .surface irregularities. However, in somecases it is desirable to produce an article of regular configuration andin particular to produce hollow slugs of silica having a smooth interiorbore. If such hollow slugs are produced by simply melting silica in acarbonaceous container around a core also `consisting of carbonaceousmate` rial, then due toexcessive heat being required to effect a'complete settling the core will be found to be firmly imbedded in thesolidified mass so that its removal is very troublesome, also numerouspockets and irregular-ities will be found on the surface of the slug. Yi

In accordance'with my present invention, I have provided a methodwhereby a smooth bore slug canbe conveniently and cheaply produced byforcing the core' or other molding member into 'the silica when heatingto plasticity,l the core preferably also being heated, and thenimmediately chilling vthe molded mass to prevent chemical reactionbetween the silica and the molding member. The chilling step can becarried out by merely removing the mold and silica 'from the furnaceinto the open air. With this precaution the molding member will notadhere to the silica and, therefore, may be readily removed from thesolidified article which will have a regular configuration.

My invention i s illustrated by the accom.

panyng drawing in which Fig. 1 is a seine-v rounding screws have beenmerely indicatedbythe rectangle l surrounding the tubular container 2 inwhich the fusion is carried out. These parts of the furnace aredescribed in my former Patent No. 1,549,597 issued August 11, 1925.Within the tubular containeris, suspended a refractory Crucible.

3 in which is contained a charge of quartz or silica 4. The container 3,which ordinarily consists of graphite `is threaded at its upperend andis attached to a threaded tubular support 5 by a coupling 6. The supportSis threaded vat its upper end into a cap -7 which rests on the tube 2.A

After a charge of silica in the graphite container 4 has been heated toa temperature of plasticity, Which should occur with suicient speed toprevent adhesion ofthe silica to the container, a refractory core member8 is pushed down into the plastic mass into the position shown in thedrawing. rl`he core member 8, which also may consist of graphite andwhich should have a smooth exterior is attached to a graphite rod 9traveling between suitable guides 1,0, 11 and 12 and provided with apropelling device represented by the Weight 13. T.n

lorder to get the best and cleanest product both the Crucible 3 and thecore memberB should be ,vacuum red at a high temperature, say to about200()o C. before the fusion is carried out and the core member 8preferably should be preheated to a temperature' approximating thetemperature at which silica becomes plastic which is about 1700"V` C.The preheating of the core member 8 is easily carried out by having itin a position just-above the Crucible 3 while the silica is being heatedto plasticity. The bottom of the crucible preferably is perforated asindicated at 14 in order to permit gas to escape and preferably isprovided with a depression into which the pointed end of the core member8 is brought to bear.

When lthe core 8 hasv been introduced into the plastic silica then theCrucible is imme- Sti diately removed from the furnace, for example, bywithdrawing the entire structure supported bythe tube 5. If the heatingof the silica to plasticity occurs at a sufficiently high rate and themass is not overheated very little adherence occurs between thesolidified silica and the Crucible 3. The core member 8 may be withdrawnfrom the slug leaving a smooth bore as shown in Rig. 2. The outercontainer 3 may be cracked oil1 the exterior of the hollow slug. Itscontraction upon the core makes its removal in any other wayimpracticable. There then remains as shown in Fig. 4, an article otregular interior and exterior configuration.

if it is desired 'to produceren article having' more accurate exteriorConfiguration then an exterior as well as an interior molding member maybe introduced into the plastic fusion. In the apparatus illustrated inFig. 3, the plunger introduced into the silica fusion comprises both acore member 8 and also a cylindrical exterior member l5 which lits intothe interior of the mold f3. The introduction ot this exterior member l5simultaneously with the core member 8 pushes the layer ot silicaimmediately ad- ]acent the wall crucible 3 downward to the bottom of'the crucible as indicated at 16. When the Crucible and its contents areimmediately removed from the furnace and cooled no substantial adhesionoccurs between the slugs of silica and the core members 8 and 15 so thatthe smooth regular body is produced as shown in Fig. 4. The material 16the bottom of which lis associated with a small amount of carbon may becut oil and rejected.

It should be understood that ,y various changes and modifications may bemade in carrying out my invention. or example, the molding member may beintroduced with a motion other than rectilinear and may be shaped tomold the quartz fusioninto forms more complex than a simple cylinder.

What I claim as new and desire to secure by Letters Patent of the UnitedStates 1. vThe method of producing a hollow silica article whichconsists in heating a' in place, the cooling occurring with suflicientrapidity after introduction of the Core member to prevent adhesion ofthe charge and core member and finally removing the mold and core fromthe solidified charge.

2. The method of producing hollow slugs oi silica which consists inheating a charge of silica to about 1.7000 C. in a v graphite container,pcrforating the plastic mass with :1 graphite plunger. cooling saidCharge belore adhesion of the plunger to the silica has occurred,withdrawinc the lunger from the solidified charge and lireakmg away thecontainer from the Charge.

3. The method of producing a tubular body of silica which consists inmolding plastic silica between a core and shell of refractory material,cooling said silica in situ to a solidifying temperature with sufiicientpromptness after molding to prevent adhesion of the silica to the Coreand shell and withdrawing said molding membersV from the solidifiedmaterial.

4. The method of reducing a hollow silica body which consists inintroducing a graphite molding member into a charge of plastic silica,cooling said charge with sufcient promptne'ss to revent adhesion ot saidmember to the silica and withdrawing the molding member from thesolidified silica.

in witness whereof I have hereunto set my hand this 20th day of November1925.

LEVI B. MILLER.

